diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2021-09-28 14:24:32 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-10-05 15:52:09 +0200 |
| commit | 8d491de6edc27138806cae6e8eca455beb325b62 (patch) | |
| tree | 63a9b2be7c7f2baacc8dfd695088634fd1c8d079 | |
| parent | d07b2eee4501c393cbf5bfcad36143310cfd72f9 (diff) | |
| download | linux-8d491de6edc27138806cae6e8eca455beb325b62.tar.bz2 | |
sched: Move mmdrop to RCU on RT
mmdrop() is invoked from finish_task_switch() by the incoming task to drop
the mm which was handed over by the previous task. mmdrop() can be quite
expensive which prevents an incoming real-time task from getting useful
work done.
Provide mmdrop_sched() which maps to mmdrop() on !RT kernels. On RT kernels
it delagates the eventually required invocation of __mmdrop() to RCU.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210928122411.648582026@linutronix.de
| -rw-r--r-- | include/linux/mm_types.h | 4 | ||||
| -rw-r--r-- | include/linux/sched/mm.h | 29 | ||||
| -rw-r--r-- | kernel/sched/core.c | 2 |
3 files changed, 34 insertions, 1 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 7f8ee09c711f..e9672de22cf2 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -12,6 +12,7 @@ #include <linux/completion.h> #include <linux/cpumask.h> #include <linux/uprobes.h> +#include <linux/rcupdate.h> #include <linux/page-flags-layout.h> #include <linux/workqueue.h> #include <linux/seqlock.h> @@ -572,6 +573,9 @@ struct mm_struct { bool tlb_flush_batched; #endif struct uprobes_state uprobes_state; +#ifdef CONFIG_PREEMPT_RT + struct rcu_head delayed_drop; +#endif #ifdef CONFIG_HUGETLB_PAGE atomic_long_t hugetlb_usage; #endif diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index 5561486fddef..aca874d33fe6 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -49,6 +49,35 @@ static inline void mmdrop(struct mm_struct *mm) __mmdrop(mm); } +#ifdef CONFIG_PREEMPT_RT +/* + * RCU callback for delayed mm drop. Not strictly RCU, but call_rcu() is + * by far the least expensive way to do that. + */ +static inline void __mmdrop_delayed(struct rcu_head *rhp) +{ + struct mm_struct *mm = container_of(rhp, struct mm_struct, delayed_drop); + + __mmdrop(mm); +} + +/* + * Invoked from finish_task_switch(). Delegates the heavy lifting on RT + * kernels via RCU. + */ +static inline void mmdrop_sched(struct mm_struct *mm) +{ + /* Provides a full memory barrier. See mmdrop() */ + if (atomic_dec_and_test(&mm->mm_count)) + call_rcu(&mm->delayed_drop, __mmdrop_delayed); +} +#else +static inline void mmdrop_sched(struct mm_struct *mm) +{ + mmdrop(mm); +} +#endif + /** * mmget() - Pin the address space associated with a &struct mm_struct. * @mm: The address space to pin. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 95f4e16f98a2..9eaeba671001 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4836,7 +4836,7 @@ static struct rq *finish_task_switch(struct task_struct *prev) */ if (mm) { membarrier_mm_sync_core_before_usermode(mm); - mmdrop(mm); + mmdrop_sched(mm); } if (unlikely(prev_state == TASK_DEAD)) { if (prev->sched_class->task_dead) |